Temperature responsive current regulating means



Aug. 9, 1949. w. c. SEALEY TEMPERATURE RESPONSIVE CURRENT REGULATING MEANS Filed NOV. 9, 1945 .SJJi

-aa '-za -/0 AME/EN? rEMPERATa/Pg //Y a Patented Aug. 9, 1949 UNITED STAT ES OFFICE TEMPERATURE RESPONS IVE' CURRENT REGULATING MEANS William C. Sealey, Wauwatos'a, Wis., assignor to Allis-Chalmers Manufacturing. Company; Mil waukee, Wi s., a corporation of Delaware Application November 9, 1945; Serial No: 627;725

6 Claims. 1 Thisinvention relates in general to'electrical control-systems and relates particularly to control-systems in which the controlling elements-are susceptible to changes in temperature.

In prior art control systems of the type utilized for controlling the voltage of a circuit, a contactmaking voltmeter has been utilized to initiate regulating action. Such contact making voltmeteror voltage responsive relay has been connected to measure the regulated voltage, and is balanced against a biasing force when the regulated voltage is at the normal desired value. A

contact making voltmeter of this type may beexposed to temperatures which may range from minus forty to sixty degrees centigrade. Such changes in temperature will change the resistance' of the coil of a contact making voltmeter, causing more or less force to be applied against the" biasing force when the same voltage is applied thereto, so that the contact makingvoltmeter' will not remain in balanced condition when the regulated voltage is at normal desired value.

Itis therefore an object of the present invention to provide an improved control system for an electrical current carrying winding, such control system providing compensation for changes inwinding resistance due to changes in temperature of the winding.

It is a further object of the present invention to provide an improved temperature compensation control for a voltage responsive winding in which a substantially constant current is maintained when the voltage to which the winding is responsive is at a constant value.

It is a further object of the present invention to provide a temperature compensated voltage responsive winding with further improved temperature compensation actuated by thermal switches exposed to the temperature changes for which the winding is compensated.

It is also an object of the present invention to' provide an improved voltage regulating system that is accurate when the controlling elements are exposed to changes in temperature.

Objects and advantages other than those above set forth will be apparent from the following'description when read in connection with the accoih'panying drawing in which:

Fig. Us a diagram of connections of a voltage regulating system embodying the present invention;

Fig. 2 illustrates a characteristic curve illllS trati'ngthe relationship of various factors affecting the control system showiiiri'Fig; 1'; and

Fig. -3 isa' diagram illustrating the use of thermal switches in connection with the resistor in series with the contact making voltmeter of the system of Fig. 1. v

The invention is illustrated in connection-with a voltage regulating system'of the't'yp'e known as a tap changing under load system. Analternating current source of supply motor 8'from an energizing winding [2 through contacts 9 or ID. The motor 8 runs the tap changing switch 5 in one direction or the other to connect a greater or lesser portion of the winding6 into thecircuit; The winding 6 is connected'into-the circuit by one or more of the con-' tacts I6 through the contacts of a reversing switch l5 and through a preventive autotransformer MI The contact making voltmeter 1 is shown in its balanced position in which the mag-' netic effect'of the winding 25 balances the force of'gravity acting on the core of the contact making voltmeter'l, or other suitable bias means.

The control system as above described would" notice as accurate as desired in some instances, where the coil 25 is subjected to changes in temperature. Outdoor installations of regulators of the typeshown may be subjected to temperatures ranging from minus forty degrees centigrade to sixty degrees centigrade. Changes in temperature would change the resistance of coil 25 and therefore a difierent value of current would balance relay 1 at high temperatures than would balance the relay 1 at low temperatures.

In order to maintain the current in coil 25 at a substantially constantvalue when the relay 1: is j in a balanced condition, independently of changesin ambient temperature, the coil 25 is shunted by a resistor l8 having a high temperature coefiicient of resistance and has connected in series therewith a resistor ll having a low or negative-temperature coefiicient of resistance.

Thus-if the ambient temperature should in-- creasjtheresistance of coil 25 and of resistor l 8will"increase and the resistance of resistor l'l The rewill remain thesame or'wi-ll decrease.

the drawing in sistance of resistor I8 will increase more, for a given temperature change than will the resistance of coil 25. Therefore, upon a rise in ambient temperature, the same or a slightly greater value of voltage will be applied to the coil 25 by the coil I3 when the regulated voltage is at the normal desired value. However because of the variation of resistance in the shunt circuit elements, due to temperature change, more current will flow through the coil 25 and less through resistor I8 than would if the ambient temperature was at a lower value.

Conversely, if the ambient temperature drops, the resistance of coil 25 and of resistor I8 will decrease, and the resistance of resistor M will remain the same or increase, and the same or less voltage will be applied to the winding 25 by the winding I3 when the regulated voltage is at the normal desired value. However the resistance of resistor I8 will decrease in value more than the resistance of coil 25 and hence a greater portion of the current supplied to the shunt circuit will flow through the resistor I8, thus causing less current to flow through the coil 25. With temperature compensation as above outlined, the relationship between the voltage required to balance the circuit and the ambient temperature is as shown by the curve A-D in Fig. 2.

To further improve the accuracy of the control system, thermally responsive switches 2I and 22 are provided as shown to remove shunts from portions I9 or 20 of the resistor I8 when the ambient temperature has risen to certain predetermined values.

As the ambient temperature rises to a value shown in Fig. 2 as point C, which is shown as 35 degrees centigrade, the thermal switch 2I will open its contact, as shown, thereby removing a shunt around the portion I9 of the resistor I8. Addition of the portion I9 into the circuit shunting the coil 25 permits the available voltage to cause relatively more current to flow through the winding 25 than flows through resistors I8 and I9, so that less voltage is necessary to balance the circuit. As shown in Fig. 2, upon opening of the switch 2I, the voltage necessary to balance the circuit drops from about 120.15 volts at point C to 119.8 volts at the point E. As the ambient temperature continues to rise, the voltage necessary to balance the circuit follows the curve EF rather than the curve CD. When the ambient temperature reaches a second predetermined value, shown in the curve of Fig. 2 as fifty degrees centigrade, the thermal switch 22 similarly opens its contact, opening the shunt about the portion 28 of the resistor I8, thereby again dropping the voltage necessary to balance the circuit, as shown in Fig. 2, to the point G.

It is thus seen that with the improved compensation provided by the action of the thermal switches 2 I, 22, the current in the coil 25 is maintained at a substantially constant value when the regulated voltage is at the normal desired value. The band Width in which the relay will remain balanced, extends from 119.? volts to 120.2 volts or a band width of approximately half a Volt. 7

By way of example a satisfactory embodiment of the invention has been utilized in which the thermal switches 2|, 22 were set to operate at forty degrees centigrade and fifty degrees centigrade. In this embodiment the resistor I8 was of a high temperature coeflicient material, and had a resistance of the order of 500 ohms. The portions I9 and 20 of resistor I8 each had a resistance of the order of 10 ohms. The resistor IT was made of a substantially zero coefllcient of resistance and had a resistance of the order of 400 ohms. The winding 25 had a resistance of the order of 50 ohms. The above example is included in an illustrative rather than a limiting sense.

Although the correction efiected by the thermal switches has been illustrated in connection with the shunt resistor I8, such thermal switches could as well act to shunt a portion of the series resistor H as shown in Fig. 3. The thermal switches would then operate in the opposite sense, that is, would close their contacts 26 and 21 (when working on the right hand side of the curve of Fig. 2) upon increase in temperature, thereby shunting portions 28 and 29 of resistor I'I.

The resistors I8 and H are most effective when the temperature coefilcients are as above described. The compensation would be efiected, with additional thermal switches, if the resistors had positive, negative or zero temperature coefficients of resistance or any combination of such coefficients.

Although but two embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a system comprising a source of electric current for supplying current to a conductor having a predetermined temperature coeflicient of resistance, the combination of said conductor with means connecting said conductor with said source, and means for reducing the variations of the current in said conductor caused by ambient temperature changes comprising a resistor having a temperature coefilcient of resistance which is lower than the temperature coeflicient of resistance of said conductor serially connected with said source and said conductor, another resistor connected in shunt with said conductor, and means in addition to the temperature coefilcient variation responsive to ambient temperature for varying the efiective value of one of the said resistors to thereby vary the voltage drops in said resistors and in said conductor.

2. In a system comprising a source of electric current for supplying current to a conductor having a predetermined temperature coefiic'ient of resistance, the combination of said conductor with means connecting said conductor with said source, and means for reducing the variations of the current in said conductor caused by ambient temperature changes comprising a resistor serially connected with said source and said conductor, another resistor having a temperature coeflicient of resistance which is higher than the temperature coeflicient of resistance of said conductor connected in shunt with said conductor, and means in addition to the temperature coefllcient variation responsive to ambient temperature for varying the effective value of one of said resistors to thereby vary the voltage drops in said resistors and in said conductor.

3. In a system comprising a source of electric current for supplying current to a conductor having a positive temperature coefficient of resistance, the combination of said conductor with means connecting said conductor with said source, and means for reducing the variations of the current in said conductor caused by ambient temperature changes comprising a resistor serially connected with said source and said conductor, another resistor having a temperature coeflicient of resistance which is higher than the temperature coefficient of resistance of said conductor connected in shunt with said conductor, and means in addition to the temperature coeincient variation responsive to ambient temperature for varying the effective value of the said shunt connected resistor to thereby vary the voltage drops in said resistors and in said conductor.

4. In a system comprising a source of electric current for supplying current to a conductor having a positive temperature coeflicient of resistance, the combination of said conductor with means connecting said conductor with said source, and means for reducing the variations of the current in said conductor caused by ambient temperature changes comprising a resistor having a temperature coefficient of resistance which is higher than the temperature coefficient of resistance of said conductor connected in shunt with said conductor, another resistor having a temperature coeflicient of resistance which is lower than the temperature coeiiicient of resistance of said conductor connected in series with said source and said conductor, and means in addition to the temperature coefiic'ient variation responsive to ambient temperature for vary- 6 ance, the combination of said conductor with means connecting said conductor with said source, and means for reducing the variations of the current in the said conductor caused by ambient temperature changes comprising a resistor havim a temperature coeficient of resistance which is higher than the temperature coefficient of resistance of said conductor connected in shunt with said conductor, another resistor having a zero temperature coeflicient to resistance connected in series with said source and said conductor, and means in addition to the temperature coefficient variation responsive to ambient temperature for varying the effective value of said shunt connected resistor.

6. In a system comprising a source of electric current for supplying current to a conductor having a positive temperature coeflicient of resistance, the combination of said conductor with means connecting said conductor with said source, and means for reducing the variations of the current in said conductor caused by ambient temperature changes comprising a resistor having a temperature coefficient of resistance which is higher than the temperature coefiicient of resistance of said conductor connected in shunt with said conductor, another resistor having a negative temperature coefiicient of resistance connected in series with said source and said conductor, and means in addition to the temperature coefficient variation responsive to ambient temperature for varying the effective value of said shunt connected resistor.

WILLIAM C. SEALEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,411,311 Sullivan Apr. 4, 1922 2,022,874 West Dec. 3, 1935 2,083,387 Merrill June 8, 1937 

